1. Field of the Invention
The present invention relates to a magnetic tape cassette, and particularly relates to an original compact magentic tape cassette whose size is not larger than a magnetic tape cassette of the Philips type and which is used for an audio equipment or the like.
2. Background of the Invention
In recent years, the size and weight of a cassette tape recorder have been reduced. A compact magnetic tape cassette has become widely used for the cassette tape recorder of reduced size and weight. In the field of audio equipment, a magnetic tape cassette has become strongly desired which is usable for recording and reproduction of high quality and density for a long time. A type of magnetic tape cassette which meets this desire is widely known as a magnetic tape cassette of the digital type such as the pulse code modulation (PCM), in which an input signal is converted into pulses for recording and reproduction in an operation different from the analog type.
Nowadays, a large video tape cassette has become generally used as a magnetic tape cassette of the digital type. In this large video tape cassette, the recorded frequency band is made wider than that for a conventional audio tape cassette because the recorded frequency band for the large video tape cassette needs to be made about five times wider than that for the conventional audio tape cassette. The large video tape cassette is recorded and played with a rotary-head system (except for special cases) and has such a construction that an opening provided in the front of the cassette may be closed with a guard panel which is openable upwardly from the cassette. Since the large video tape cassette is of the digital type, recording and reproduction of high density and wide frequency band are performed with a shorter recorded wavelength for the cassette than for a conventional compact audio tape cassette. For that reason, the video tape cassette requires a design in which dust-proofing and tape protection measures are taken.
The magnetic tape cassette, to which the present invention relates and which meets the above-mentioned desire, can be used for an audio equipment of the like for which a recording/reproduction system of relatively wide frequency band is adopted and can be used as well as the above-described video tape cassette. The size of the magnetic tape cassette is no larger than that of the conventional compact audio tape cassette and is therefore very small. For that reason, the magnetic tape cassette is expected to be carried and used outdoors as frequently as the conventional compact audio tape cassette. Consequently, the magnetic tape cassette has been required to have such construction that a high dustproof protection is achieved with a dustproof mechanism that does not improperly operate, and tape jamming or the like is reliably prevented from occurring due to tape looseness caused by the vibration of the cassette during its carrying or the like.
One of magnetic tape cassettes proposed to meet the above-mentioned requirement is provided with a locking member so that hubs on which a magnetic tape is wound are locked or unlocked by the locking member when the tape is put in use or out of use. The locking member is always urged toward the hubs by a spring so that sharp-pointed projections provided on the locking member come into contact with the hubs to hinder their rotation when the tape is not in use. The projections are separated from the hubs when the tape is in use. The locking member has arms extending in opposition to the sharp-pointed projections. Claws are provided on the tip portions of the arms so that the claws extend rightward and leftward. When a guard panel is turned in such a direction as to open the front of the cassette, locking portions protrusively provided on the inner surfaces of both side walls of the guard panel slide the locking member in the forward direction of the cassette while engaging with the claws, to disengage the sharp-pointed projections from the hubs. When the hubs are unlocked, the arms of the locking member slide on a lower half casing and a flat portion having the sharp-pointed projections moves near the inside surfce of an upper half casing. For that purpose, each of the arms and the flat portion are located at a distance from each other nearly equal to the depth of the interior of the cassette. The spring acts on the flat portion to urge the locking member in such a direction as to lock the hubs.
To assemble the magnetic tape cassette, some members are sequentially set in the lower half casing. Since the spring for urging the locking member acts between the upper half casing and the locking member, the assembly is performed as the locking member remains urged by the spring and fitted to the upper half casing. However, if the lower half casing, in which the hubs with the magnetic tape would thereon are set and the upper half casing, fitted with the locking member, were assembled with each other as they were, the sharp-pointed projections would be over-laid on the hubs because the locking member is urged to such a position as to lock the hubs. For that reason, the guard panel is fitted to the upper half casing. Then, the panel is turned so that the locking member is pulled out to such a position as to unlock the hubs. The upper half casing is thereafter assembled with the lower half casing.
A prism receives light from a tape-detecting light emission element in a recording/reproduction machine, refracts the light and reflects it to a light reception element. The prism is located in the upper half casing so that the prism is located in a more internal position than a predetermined magnetic tape movement path. As a result, the magnetic tape does not come into contact with the prism when the tape is moved for recording and reproduction.
At the time of the above-described assembly, the magnetic tape is wound on one of the two hubs and tightly supported on a pair of tape guide members provided in the lower half casing at both the sides of the front opening thereof. A leader tape secured to the hub on which the magnetic tape is not wound is tightly supported between the hub and the tape guide member in a more internal position (line A of FIG. 1) than the predetermined magnetic tape movement path. When the upper half casing is assembled with the lower half casing, it is likely that the leader tape will contact the prism provided in the upper half casing and be guided along the oblique reflecting surface of the prism and forced to a more internal position (line C) than the prism thereby making it possible to locate the magnetic tape and smoothly move it to it's correction position. This has become a significant problem in cassette assembly.
Such a problem also occurs in the so-called C-O winding method in which hubs are assembled to construct magnetic tape cassette and a magnetic tape is thereafter wound on the hubs.